The increasing proliferation of mobile communication devices is accompanied by an increasing desire by users for flexibility in their communications. One widely used approach is the formation of groups of mobile devices; formation of such groups allows communication between mobile devices without a need for participation by a base station in organization or management of the group. Data between group members is typically secured using a shared symmetric key, known by all current group members. Group management may be accomplished by one of the group members, suitably referred to as a group manager. The group manager distributes the key to new members joining the group and renews the key when a device leaves or is revoked from the group. Each mobile device can belong to multiple groups and the group manger may manage multiple groups.
Group communication may be performed, for example, through a wireless multi-hop broadcast medium. The organization of the group typically allows for communication between group members without previous planning, so that meeting times between group members and availability of group members are difficult to predict. When a key needs to be renewed, only a subset of a group's members might be available, with others being out of range or turned off.